1. Field of the Invention
The present invention relates to a magnetic bearing arrangement for a rotor having permanent magnets to absorb the radial bearing forces, and having a stabilizer which holds the rotor in a contactless position in relation to a stator. Electric coils attached to the stator thereby interact with magnetizable parts fastened on the rotor.
2. Description of the Prior Art
Magnetic bearings of this type are described in U.S. Pat. No. 3,929,390 and the "Journal of Spacecraft", Volume 17, No. 2, 1980, pp. 93-98, both of which are hereby expressly incorporated by reference, with the same effect as if their entire contents were fully set forth herein. On these magnetic bearings, ring-shaped permanent magnets are attached to both rotor ends, and interact with ring magnets fastened on the stator, so that a radial centering force is exerted on the rotor when a radial excursion occurs. Simultaneously, a force instability arises in the axial direction as a result of the permanent magnets. This force instability is compensated by an electromagnetic deflection cell which is attached in the middle of the rotor and acts axially, and which is fed electrical control currents as a function of the current axial deflection of the rotor from its specified axial position. The deflection is measured by means of a contactless sensor system, which regulates the control current flowing through the deflection cell by means of a corresponding electric amplifier. On both sides of the deflection cell, in the immediate vicinity of the permanent magnets attached to the ends of the rotor, there are copper discs rigidly connected to the stator, which interact with permanent magnets fastened on the rotor so that the radial vibrations of the rotor are damped. On the other hand, in a magnetic bearing arrangement described in German Published Patent Application No. 34 09 047, there are permanent magnetic bearing elements which produce a radial centering of the rotor, which essentially occupy positions on both sides of the rotor center-of-gravity, while the deflection cell on the end of the rotor shaft is placed outside the permanent magnet rotor bearing. The deflection cell thereby contains several permanent magnets fastened on the rotor, which interact with a copper plate attached to the stator to produce an eddy current damping for radial vibrations of the rotor.
A disadvantage of the magnetic bearing arrangements described above is that, during the operation of such bearing arrangements, axial deformations of the rotor occur, as do, to a particular extent, axial deformations of the housing enclosing the rotor, to which the stator magnets are fastened. This can result in a significant maladjustment of the bearing system, such that, under unfavorable conditions, the play in the magnetic deflection cell is exceeded. The above-mentioned deformations occur in particular as a function of pressure stresses on the housing, e.g. if the housing is evacuated, or as a result of thermal stresses, which are primarily caused by the drive motor for the rotor. On the other hand, the rotor can be heated by the drive operation, or by gas friction at high rotational speeds, causing a change in the length of the rotor and thus a maladjustment of the magnetic bearing arrangements.